Surgical sutures are generally categorized as absorbable or non-absorbable depending upon whether the suture material is degraded and absorbed by the body. Both categories of sutures are made from natural or synthetic materials. Sutures are further differentiated based on whether the suture is made of a single filament (monofilament) or multiple filaments that are twisted or braided. All sutures may be provided with variety of coatings which serve to both minimize friction as the suture is passed through the tissue and to decrease tissue reactivity.
The choice of suture for a given surgical procedure is based on the properties of the suture material and the response of the tissue being repaired. However, all suture materials are at least required to be strong enough to carry the applied load, and to substantially maintain dimensional integrity after implantation.
It is well recognized that the natural response of tissue to injury, even injury resulting from a careful and appropriate surgical technique, is one of extracellular fluid accumulation (edema) in the vicinity of the wound. Thus, sutures which have been appropriately placed and tensioned at the time of surgery may operate to excessively constrict the tissue as edema forms post-operatively. Excessive constriction results in strangulation and necrosis of the tissue.
It is often difficult to anticipate at the time of surgery how much edema will form post-operatively. Thus, it is not feasible to leave sutures slack at the time of placement in the hope that subsequent edema will ensure an appropriate suture tension. Moreover, poor initial approximation resulting from the placement of a slack suture can allow entry of bacteria and contribute to wound dehiscence.
Sutures are sometimes placed in previously inflamed tissue which is edematous at the time of the surgical repair, as a result of (1) tissue inflammation and/or (2) an injection of an anesthetic and/or hemostatic agent into the wound margins. In this circumstance, the sutures are tensioned to accommodate the edematous tissue. In the immediate post-operative period, the sutures may slacken as the edema resolves. This can result in bacteria entering the wound and poor wound healing.
Proper suturing requires that the sutures be tensioned just enough to approximate, but not strangulate, the tissue. For example, in skin closure, small bites of tissue with the needle placed at 2 to 3 mm from the skin edges keeps the amount of tissue under tension relatively small, and helps to minimize scarring. Wound edema in the early post-operative period increases the tension on the skin between sutures. This frequently results in permanent skin suture marks, especially if the sutures are allowed to remain for prolonged periods. (S. J. Aston; "The Choice of Suture Material for Skin Closure". J. of Derm. Surg. 2(1): 57-61, March 1976), incorporated herein by reference.
Proper tensioning of sutures even in the hands of a skilled surgeon is difficult, subject to error, and time consuming. When a suture is tensioned too tightly, or becomes too tight as a result of tissue edema, the surgeon must cut the suture using a scalpel, scissors or laser. (Marc F. Liebermanx, "Suture Lysis by Laser and Goniolens" Am. J. Ophth. 95(2): 257-258, 1983). However, removal of a tight suture can result in gaping of the wound and subsequent scarring. Furthermore, additional time is needed to correct the problem thereby further extending the surgical procedure.
When a suture is tensioned too loosely, or there is loosening of the suture post-operatively, the suture must be replaced. This is time consuming as is the case with overly tight sutures, and in some instances may require a return to the operating room. Moreover, although intended to improve wound apposition and reduce scar formation, the replacement of sutures further traumatizes the tissues they are meant to repair.
Previous attempts at overcoming the difficulties with suture tension have included the replacement of sutures with a heat-shrinkable sleeve for vessel anastomosis. John J. Wozniak, U.S. Pat. No. 4,470,415 discloses the placement of a heat-shrinkable sleeve around the vessels to be joined and heating them with a wand or other suitable heat transmitting applicator. These heat-shrinkable sleeves suffer from a number of disadvantages. First, their use is limited to tubular members, and is of little value in other anastomoses, such as skin and cataract incision closure. Second, their placement requires the use of two ferrules, which become permanently incorporated into the wound. These ferrules can be made of degradable materials or non-degradable materials. The degradable materials mentioned, such as collagen and polyglycolate, cause an inflammatory response, which may lead to thrombosis and vascular occlusion. The non-degradable materials, such as polyethylene, can lead to foreign body reactions, or can erode into the vessels they are meant to repair, resulting in wound failure, infection, or thrombosis.
John F. Krumme, U.S. Pat. No. 4,485,816 discloses another approach to the eliminating of problems associated with suture repair. Staples made from a material having the intrinsic property of shape memory (e.g. nickel-titanium alloys) are used in place of sutures. The staples are formed at low temperatures in a shape which expedites entry into the tissue and then deformed into a tissue-gripping shape upon subsequent heating. Such staples are disadvantageous because, like conventional suture techniques, once inserted and deformed into a tissue-gripping shape, the tension of the staples cannot be adjusted.
Because of the difficulties in obtaining proper suture tension both intra-operatively and post-operatively using conventional sutures and alternatives including, staples and heat shrinkable sleeves as described above, there remains a need for the development of an easy to use suture whose dimensions, particularly the linear dimension can be altered after implantation in the tissue or prosthetic material.
It is therefore an object of the present invention to provide a suture whose dimensions can be altered after implantation to relieve or increase tension on the tissue or prosthetic material.
It is another object of the present invention to increase or decrease the cross-sectional area of the suture to prevent leakage around the insertion site in the anastomoses of fluid containing structures such as blood vessels, bowel and meninges.
It is a further object of the invention to provide a suture whose dimensions can be altered by the application of energy without damaging the tissue.
It is a further object of the invention to provide a method of suturing tissues or prosthetic materials employing a suture whose dimensions can be altered after implantation either at the time of surgery or in the post-operative period.